1. Field of the Invention
The present invention is related to a radiation-sensitive high-polymeric material of positive type suitable for forming micro-patterns upon manufacturing semiconductor devices such as LSIs (large scale integrated circuits).
2. Description of the Prior Art
It has been well known that radiation-sensitive materials of some kinds show such a property that portions thereof having been irradiated by radioactive rays such as electron beams, X-rays, .gamma.-rays, .alpha.-rays, ionic-rays or the like become soluble in developer. This property has been utilized for forming micro or fine patterns of semiconductor devices such as LSIs.
Generally speaking, radiation-sensitive materials of positive type as resists used on forming micro patterns are required to have good properties in sensitivity, resolution, resistivity against etching, ease of application, ease of filtering and stability.
Although there has been known polymethyl methacrylate (hereinafter referred to as PMMA), polybutene-1-sulphone or the like as a radiation-sensitive material to be used, these materials have relatively low sensitivity in general. Even PMMA having a low sensitivity of an order of 10.sup.-4 C/cm.sup.2 is considered to satisfy the properties mentioned above. Accordingly, it is needed to increase the irradiation of the radioactive rays, otherwise it takes a long time to form micro-patterns.
These micro-patterns are formed usually with use of a difference between solubilities of irradiated and non-irradiated portions against a developer, which is caused due to a difference between molecular weights of the two portions. However, when a film of PMMA applied on a substrate is heated to dry, every molecule of PMMA is oriented in one direction and, due to this, there is not caused a sufficient difference in the solubility against the developer between portions irradiated by radioactive rays and portions not irradiated. Consequently, it becomes difficult to form clear micro-patterns. In other words, the sensitivity of the film to radioactive rays is lowered by heating thereof and in order to form micro patterns clearly, much more radioactive rays and/or a longer radiation time are required. However, this lowers the through put in the production of such devices. Thus, radiation-sensitive materials having a higher sensitivity are demanded.
One might consider increasing the molecular weight of PMMA in the initial state (namely, before exposure to radioactive rays) in order to enhance the sensitivity thereof since it helps make the difference in the solubility large.
However, this causes such disadvantages that it becomes difficult to apply a film with a uniform thickness and to remove contaminations since the ease of application and ease of filtering thereof are lowered thereby.
In JP-A (Japanese Patent Laid Open Publication) No. 82241/1983, there is proposed a radiation-sensitive material having a high sensitivity which is improved by adding a halogenated compound of alkyl ammonium to PMMA represented by the formula R.sub.4 NX (R means an alkyl group and X means a halogen atom). The radiation sensitivity thereof is improved to a degree of 5.times.10.sup.-6 C/cm.sup.2, but it is not sufficient for practical use. Further, in JP-A No. 163233/1982, there is proposed a radiation-sensitive material having a radiation sensitivity of a degree of 1.times.10.sup.-6 C/cm.sup.2 in which tetraalkyl ammonium perchlorate selected from among halogenated compounds of alkyl ammonium is added to PMMA. However, this material is inferior because ease of filtering depends on a molecular weight thereof and, therefore, contaminants cannot be removed. Further, it is not suitable for practical use because it is difficult to form a film having a uniform thickness due to the quick drying property of methyl ethyl ketone used as a solvent for PMMA.